The use of calibration reference phantoms for use with computerized tomography (CT) systems has been clinically demonstrated at the University of California, San Francisco, to provide substantial enhancement in the utilization of such systems for bone density measurements. Such quantitative computer tomography (QCT) systems have in more than 300 clinical installations, provided early detection and precise long-term monitoring of osteoporosis patients. The original patent for the calibration phantom is (U.S. Pat. No. 4,233,507--Donald J. Volz) disclosed the general technique of using a calibration phantom scanned simultaneously with the patient. As described in this patent, the phantom is located underneath the patient and it and the patient are scanned simultaneously with the CT scanner thus providing a standard reference for correction of various technical factors in the CT process for improved performance. The phantom provides a series of reference elements whose graduated densities correspond to varying human bone mineral contents such that the operator can manually (or more recently with a preprogrammed computer) calculate the bone mineral density of the patient.